The fabrication of monolayers of insoluble particles to the gas-liquid interface was realized through uses of troughs usually full of aqueous solutions. To the gas-water interface, solutions containing amphiphilic molecules are usually spreaded, these being molecules made of a polar head and a chain of fatty acids. After the volatile solvent has evaporated, it leaves at the gas-liquid interface the amphiphilic molecules. Finally, a mobile barrier compresses the molecules in a monolayer. Therefore, essentially there occurs an immobile trough containing an unmoving subphase or which molecules are laterally transported through it by exploiting the surface tension difference between the subphase and the deposited solution, and a mobile barrier.
The transfer of the monolayer onto a solid substrate is realized through several methods. One is the so-called Langmuir-Blodgett method, and essentially comprises a vertical immersion of a solid plate in the subphase through the monolayer; by pulling up such plate, the layer is transferred onto the plate by lateral compression. That can be repeated many times. Another method, called the Langmuir-Schaeffer method, comprises the descent of an horizontal plate onto the monolayer. After a contact is made, the plate is again extracted with the monolayer on it.
In order to improve the fabrication of insoluble particles, several attempts have been carried out. One has been to make a cylinder rotate under the water surface. One expected that such movement drove the insoluble particles ahead in a forming monolayer. However, in the majority of cases, this technique requires a precompression of an already prepared monolayer. The cylinder that compresses the layer is made of hydrophobic material. Moreover, only insoluble molecules are usable. Another device has been recently disclosed by G. Fuller, C. Franck and C. Robertson (Langmuir, 10, 1251 (1994)). It comprises the compression of insoluble particles with a flowing subphase between a fixed surface and the monolayer surfaces. Again, only insoluble molecules are used.
There are several limits in these previous methods: the essential one is that these methods are provided for insoluble particles. The attempts to extend the above methods to soluble particles have supplied marginal results. Slowness, loss of particles, low reproducibility and denaturation of proteins are a general characteristic of these methods.
The Applicant of the present invention and others disclosed a new method in the course of 1997 (Picard G., Nevernov I., Alliata D. and Pazdernick L., Langmuir, 13, 264 (1997)). The method has been marked with the acronym DTLF (Dynamic Thin Laminar Flow), and comprises a rotary cylinder that compresses a monolayer of soluble proteins. It was specifically planned in order to manufacture monolayers of soluble proteins, even if monolayers of soluble particles can also be easily realized. The features of this DTLF method are high-speed production, low amounts of materials being used, continuous production and preparation of bidimensional crystals. The newly prepared monolayer can also be deposited for further analysis on a solid, unmoving substrate. In other words, the device can be moved on a fixed substrate in order to deposit monolayers.
Even if in this study a machine has been disclosed that proved to be functional with proteins, the basic principles governing the DTLF method were not explained. This means that the use of such apparatus can be even useless if the basic forces are not controlled.